Field of the Invention
The present invention relates to an X-ray detector detecting X-ray image data for each module.
Description of the Related Art
A single-photon counting-type detector was originally used as a point sensor in order to verify the presence or absence of X-rays while discriminating energy. In such a detector, information about the incidence direction and position of X-rays was obtained by moving the sensor itself. In the early days, the arrangement of a large number of point sensors involved technical difficulties. However, the progress in semiconductor mounting technologies has made it possible to linearly (one-dimensionally) or planarly (two-dimensionally) arrange sensors and its readout circuits.
Until now, as a radiation detector in place of an X-ray film or an imaging plate, a flat panel detector using a CMOS image sensor, a CCD detector using multiple CCD devices, and the like have been usually used as a detector with a large detection surface. However, each of these is a charge storage type detector in which a detection pixel has a relatively simple structure.
The single-photon counting type detector, unlike the charge storage type detector, can discriminate an incident photon with respect to a specific energy. The single-photon counting type detector is effectively used in particular in analytical methods using X-ray diffraction because it has advantages of no background noise and a wide dynamic range.
In contrast, by two-dimensionally configuring such a detector through the use of a large number of fine pixels, the information about the position, angle and direction of incident X-rays can be extracted as the positional information on the detector without moving a detection sensor. Because of this, a data read rate (frame rate) can be improved significantly.
As the method of configuring such a detector by using multiple pixels, a hybrid method is known. In the hybrid method, for example, a pixel output terminal of each detection element of a semiconductor device and a pixel input terminal of a readout circuit are connected to each other one by one. This connection is typically made by bump bonding by using a fine solder ball. Thus, the detection element and the readout circuit are produced as separate elements and the both are connected to constitute the detector.
In such a hybrid type detector, for either the detection element or the readout circuit, the semiconductor area that can be formed is limited, and thus it is difficult to integrally form a detection surface having a large area. This is due to the influence of the yield in semiconductor manufacturing, the limit of the available wafer size, and the like. Therefore, by fabricating a detection module of a manufacturable detection area and arranging a plurality of these detection modules, a method is employed for securing a required detection area.
In the hybrid type detector, usually, a detection element and a readout circuit are bump-bonded to each other and the size of a solder ball forming a bump is also extremely small. Therefore, the detector is susceptible to an impact. Moreover, if a detection element surface has a scratch, accurate detection cannot be performed, and thus the detection element surface itself needs to avoid the handling causing a scratch or the like. Furthermore, since wire bonding may be performed on the readout circuit, for example, a special care needs to be taken for handling at the time of assembling with respect to a detection portion.
As such a hybrid type detector, US Patent Application Publication No. 2009/0218500 specification (Patent Document 1) discloses a detector, in which an X-ray detection module is held by a frame. This frame is provided with equally spaced rails for the purpose of securing the flatness of the detection region and securing a relative position with regard to the arrangement of each individual module. In addition, U.S. Pat. No. 7,514,688 (Patent Document 2) refers to a sensor module made up of N×M array of photo detection diodes and N×M array of readout unit cells and to an imaging device in which these modules are arranged in a V×W array.
However, when attempting to arrange N×M detection modules on the frame described in Patent Document 1, the work load increases. For example, in installing the modules starting from a module at a corner of the top end, each of the adjacent modules has to be installed while being positioned.
Moreover, in replacing a module located in the middle, only this module cannot be removed. After starting to remove modules from one end and once removing a large number of modules, a target module has to be removed. Also in this case, naturally, after the removal and replacement of a module, another module has to be removed while positioning the same again.
Even the detector described in Patent Document 2 cannot resolve the above-described problem. Patent Document 2 does not clearly state a specific method of installing each module. Therefore, in the conventional art, in arranging and installing N×M modules at the beginning and in removing and reinstalling any module after the arrangement, the workability decreases significantly.
In contrast, the detection region in such a detection module is a photodiode surface of a semiconductor, and is usually subjected to metal evaporation in order to apply an electric field for detection. Examples of typical metals used in evaporation include aluminum. The photodiode itself is thin (typically, several hundred μm) and is susceptible to a mechanical stress. Although bump bonding may be performed between a photodiode and a readout element, each individual bump itself in this case is extremely small (typically, several ten μm) and is also is susceptible to a mechanical stress.
In view of such circumstances, great care is required in handling a portion from a detection region to a readout element. In the detector described in the above-described Patent Documents, neither a countermeasure to protect the detection surface of a module during installing work of the module nor a countermeasure in terms of mechanism for avoiding breakage or failure caused by bringing the modules into contact with each other is implemented.